When the Irish choreographer and director Michael Keegan-Dolan was 17 he was sent to meet a guidance counsellor priest to talk about his future. Keegan-Dolan was "the only boy at school who wanted to dance". There had been fights. "I came from an incredibly bright family full of doctors, architects, lawyers and civil servants and I felt like an alien," he recalls. So he explained to the priest that he wanted to do something with his life that he feared "people wouldn't appreciate". "And the priest assumed what I meant by that was that I wanted to join the priesthood," Keegan-Dolan laughs. "I was instantly invited to a fucking retreat. Of course that's not what I meant, but 25 years on I now think there maybe isn't a whole lot of difference between being a priest and being a dancer. For me it's about a spiritual practice, it's a way of life, and when I'm dancing I'm praying. It's not about showing off or looking good, it's about connecting with something that is not necessarily tangible."

Over the last 25 years Keegan-Dolan has worked as a dancer and choreographer across a wide range of theatre, dance and opera projects. But it is with the company he founded, Fabulous Beast, that he has produced his most idiosyncratic body of work, one that has embraced Irish history, music and literature as well as classic pieces from around the world. In recent years his productions of Giselle – transfigured as a line-dancing teacher in the Irish Midlands – and The Bull – an ancient Irish folk tale twisted to castigate the Celtic Tiger economy – have both been nominated for Olivier awards, as was his 2009 English National Opera production of Stravinsky's The Rite of Spring. Keegan-Dolan now returns to the ENO to direct a new production of Handel's Julius Caesar conducted by Christian Curnyn and featuring the countertenor Lawrence Zazzo as Caesar and Anna Christy as Cleopatra.

"I know the opera form pretty well now and have strong views about what I think is good and what is not so good," he says. "And when I first came to this opera I actually wasn't sure whether we should have any dancers in it at all. Technically, there is no dance music. But when you listen to it you realise that even though Handel didn't write it with dance in mind, an awful lot of this music has come from dance rhythms. So I said let's give it a try. Let's see what gives. Handel for me is like Mozart and Rameau in that their writing is almost divine. I know Handel wrote a lot of actual holy music, but I don't mean holy in that way. It is just so fine and otherworldly that I didn't want to fuck with it by bringing in a whole lot of people dancing."

Four weeks of rehearsals with a piano and 10 dancers established "which arias could have a choreographic language and which couldn't". But he says he was still cautious. "And then the singers arrived and we began to work together and I realised that it was going to work and it could potentially be something both different and extraordinary."

One wonders what the ENO response might have been to engaging Keegan-Dolan and then getting a production with no dance. "If I was going to tackle a great work like this it might have seemed a little odd not to use all that I have in my armoury. But people's expectations really weren't a concern to me. You can't create anything purely in expectation of the other. You have to work from an inner impulse and you see what the consequences are later."

Keegan-Dolan says from "the bits and pieces" he had picked up in childhood, he didn't much like Julius Caesar, "although that obviously comes with the disclaimer that I never met the man." He always had more sympathy for his own ancestry of "the bearded people, the Celts and pre-Celts who don't like straight roads, are a bit irrational and don't like to know what's happening next. Even though, unlike the Romans, they maybe don't make the best engineers or architects. But as I got older I realised that to be fully formed you must be both reasoned and intuitive, otherwise you risk becoming either incredibly boring or just mad. Would you rather go blind from looking at the sun or mad from looking at the moon? You don't want to do either. And I now love these characters for all their strengths and all their weaknesses. I love how the darkness woven throughout the opera collides with the staggering beauty of the music."

In the opening scene, Caesar's preliminary thoughts of a rapprochement with Pompey are abruptly superseded by the delivery of Pompey's severed head. "When my brother died of cancer, I wanted to see the body," Keegan-Dolan says. "He was only six or seven stone at the end, and my sister said that I shouldn't look but I did. And you do need to look at death. That is a good thing, and in that spirit I very stupidly watched a video on the internet during the Iraq war of this young American engineer – he wasn't even a soldier – getting his head cut off. I don't know why on earth I did it, but when you have watched you can't unwatch.

"It stays with me, and in this opera the first thing that happens is that an Egyptian general comes in with Pompey's head. You can do that in all sorts of operatic ways to make it more civilised or stylised. You can have the head in a gold box. But if you take away the layers, what we are being told is that one man has cut off another man's head. And all the while there is this relentlessly beautiful music. Beautiful darkness, beautiful violence. It's a fascinating combination to work with."

Born in Dublin in 1969, Keegan-Dolan was first smitten by dance after being taken to a Christmas pantomime, but without tuition his interest was largely confined to showing off at the disco with "some bad break-dancing and a bit of Michael Jackson, although I was getting more into David Byrne's dancing, maybe because it was that bit more interior and neurotic". When he told his father that he wanted to go to dance school in England at the age of 17, "he was worried that I would be homeless. And he might have been worried that I was also gay, although he would never say that."

Keegan-Dolan won a scholarship at the Central School of Ballet, where he trained for three years under Christopher Gable. While he was quickly employed after leaving, he said he had no interest in classical ballet – "there is a whole energetic language that is of great interest to me, but I think it has been lost in the classical ballet world" – and found himself increasingly frustrated working with other choreographers. "So I set up a company because I couldn't get a job and I just didn't fit. I never wanted to do what choreographers wanted me to do. But I couldn't back it up with technical expertise because I was 19. I still don't know why I had this sense of myself as this brilliant choreographer. It was totally unjustified and it made me very unhappy. Setting up the company was like trying to cure something in myself. Trying to stop the pain. I could now tell people what to do and I could make things unfold as I wanted them to unfold. It was really important to me. Not because I wanted to be rich or famous, but because things just had to be that way or I would die. That's what it felt like."

He says his father, who was brought up on a small farm in rural Ireland and later become a senior civil servant, had a fear of his children "returning there to dig ditches" and pointed them towards the cultures of Europe and America. But Keegan-Dolan now lives with his wife – Fabulous Beast dancer Rachel Poirier – and their two young children in the Irish Midlands, where he says he is both physically and culturally nourished. "I've always found traditional Irish dancing a bit ridiculous, but I then discovered sean-nós dancing, which is pre-Christian and pre- the Irish dancing with the hands down the side. I'm fascinated by it and connect with it, as I also profoundly connect with Irish music."

Fabulous Beast's current show, Rian, features Irish and world music as well as dance, and Keegan-Dolan says it represents him "fully coming to terms with my musical heritage. It was a seriously transformative experience about how I relate to what came before me."

Rian will soon be transferring to New York, and other future plans include a collaboration with the Irish Tony award-winning writer Enda Walsh, a Yeats project with the National Theatre of Ireland and a revival of his ENO Rite of Spring in a double bill with Petrushka at Sadler's Wells. "The work I do is rarely pure dance and I am suspicious of the divisions between music and singing and dance and theatre. Opera is where those worlds collide, and having beautiful music played in the pit, someone singing on stage and another person moving inside that music in some way makes it possible to hear the music in a new way. And when all of these things come together, another thing happens.

"The big picture is that over three and a half hours of something like Julius Caesar there should be a comprehensive exchange of energy. At the start of an aria the person singing it is in one state, and by the time they finish they are in another state. The same thing happens with the viewer. I have what feels like a memory way at the back of my brain of what dance and theatre and opera can be. You get moments and glimpses and flickers, but it's never happened yet in the way I imagine it could. God knows what will happen if I ever achieve it, but at the moment it's enough that it exists and it is what keeps me going on."